〜はもちろん・〜はもとより
not to mention, let alone, of course
Noun + はもちろん / はもとより … も
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はもちろん takes one item as obvious and adds another: 彼は英語はもちろん、中国語も話せる, "he speaks Chinese, not to mention English". The first item is the expected one; the second, with も, is the addition.
It's useful for praising things and making recommendations: この店は味はもちろん、雰囲気もいい, "the atmosphere is great, not to mention the food".
はもとより means the same and is more formal and written.
Compare はともかく, which does the opposite: it sets the first item aside instead of taking it for granted. In speech, you'll also hear it the other way round: もちろん英語も話せる, "of course he speaks English too".
Examples
彼は英語はもちろん、中国語も話せる。
He speaks Chinese, and English of course.
この店は味はもちろん、雰囲気もいい。
This place has a great atmosphere, not to mention the food.
週末はもちろん、平日も込んでいる。
It's busy on weekdays too, never mind weekends.
子どもはもちろん、大人も楽しめる。
Adults can enjoy it too, not just children.
日本国内はもちろん、海外からも注文がある。
We get orders from abroad, not just from within Japan.